What to do when my phone (Moto e4) restarts by its own.

I start having this problem for about less than 24 hours. Last night, around 12 am doing my work I decided to put a new micro sd (Lexar 64 gb uhs-1) then it was stuck at 30%. I keep restarting my phone and the same thing happens. Then, when I was about to press the power botton to open it up again, I accidentally press volume down. After a few minutes or so, I noticed my phone restarts by its own.
(I'm not sure what to do & please excuse my grammar :v - I'm still 15 yr)

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